1. Field of the Invention
This invention relates to the non-destructive testing of materials, and in particular of materials such as concrete which are essentially non-homogeneous and which, at conventional ultrasound frequencies, would produce such a high degree of scattering that commonly used ultrasound techniques are not suitable.
2. Related Art
Ultrasound frequencies used in non-destructive testing of materials and in medical investigations are commonly greater than 1 MHz, whereas in highly scattering media only relatively low frequencies, below 1 MHz in any event and, in the case of concrete for example, preferably below 500 KHz, can be used. At these lower frequencies plane wave transducers would need to be unreasonably large and, moreover, when detecting incoherent waves produced in scattering media would be subject to phase cancellation effects. Hence new techniques and devices are required which are suitable for use in connection with scattering media; and it is an object of the present invention to provide an effectively point-source transmit/receive transducer suitable for such applications and, preferably, capable of wideband operation and suitable for short pulse or chirp operation, at low-ultrasound frequencies.